Conventional electrical power systems utilize a synchronous electrical generator for generating AC power. Particularly, such a generator may include a rotor and a stator having a stator coil. In applications such as an aircraft, the rotor is driven by an engine so that electrical power is developed in the stator coil.
Aircraft power systems include plural loads to be powered. Such loads may include avionics DC loads, such as electronic systems, pulsating loads, such as radar, and AC loads, such as fans. The generator comprises a DC exciter followed by a rotating rectifier and a synchronous main generator. The AC power developed in the main generator stator coil is rectified and filtered by a ripple filter to provide DC power on a DC link. This power, which may be on the order of 270 volts DC, can be provided directly to DC loads, through DC-DC converter circuits to DC loads, or through an inverter circuit to an AC bus for powering AC loads.
The DC-DC converter circuits, discussed above, act as nearly constant power loads to the electrical power system. Any increase in voltage from the power system results in a decrease in current because the load on the supply normally demands constant current from the tightly regulated DC voltage. These negative impedance characteristics create the possibility of unstable operation of a 270 volt DC system.
The purpose of the ripple filter is to reduce the generator ripple on the DC link. To reduce the possibility of unstable operation, a damper circuit may also be included. The most commonly used damper circuit is an RC circuit connected across the DC link. The damper circuit reduces the Q of the ripple filter, reducing the peaking and output impedance. The resistor performs the damping of the filter, and the capacitor blocks the DC portion of the input voltage to reduce dissipation in the resistor. The blocking capacitor is typically larger than the ripple filter capacitor since its impedance must be small enough at the resonance of the RC filter to allow the resistor to provide effective damping at this frequency. Owing to size and weight consideration in aircraft design, it is desirable to minimize the size and weight of the ripple filter, and the damper circuit.
The present invention is intended to solve one or more of the problems discussed above in a novel and simple manner.